def Isf(list_number):
    d = list_number[1] - list_number[0]  # 求公差d
    for i in range(1, len(list_number) - 1):
        if d == list_number[i + 1] - list_number[i]:
            return '构成等差数列'
        else:
            return '不能构成等差数列'


list = eval(input('请输入一个整数数列（元素个数大于2）：'))
print('此数列', Isf(list))
